Abstract
This article presents a cryptographic key protection technique from physical security attacks through Si-backside of IC chip. Flip-chip packaging leads to a serious security hole that allows emerging backside physical security attacks. The proposed backside buried metal (BBM) structure forming a meander wire pattern on the Si-backside detects unexpected disconnection of the meander and warns the malicious attempts to expose a vulnerable Si substrate. Moreover, the BBM meander also shields key information of cryptographic circuit from both passive side-channel attacks and active laser fault injection as well. Unlike other conventional laminate-based protection, this backside monolithic approach does not require frontside wiring resources or additional packaging layers, resulting in only 0.0025% size-overhead. The BBM meander was formed on the backside of a 0.13- $\mu \text{m}$ CMOS cryptographic chip by wafer-level via-last BBM processing.
Highlights
W ITH the rapid growth of Internet of Things (IoTs) applications and devices, data security has been a major issue since IoT edge devices acquire confidential and privacy information and export it to the cloud network
It shows that the backside buried metal (BBM) meander and the through Si vias (TSVs) to frontend circuits are seamlessly formed
Since the BBM and TSVs are formed in the existing backside Si-substrate and under IO pads, respectively, our technique only requires the additional area of the disconnection detector circuit with extremely small size of 300 μm2, which is only 0.0025% of total chip area on the frontside
Summary
W ITH the rapid growth of Internet of Things (IoTs) applications and devices, data security has been a major issue since IoT edge devices acquire confidential and privacy information and export it to the cloud network. These attacks target an IC chip rather than signal wiring on-board because it is necessary for attackers to extract a cryptographic key in order to steal or tamper with data instead of destroying it. The active topmetal shield technique can be used for backside protection by bonding two dies back-to-back [8] and, a breakable die with an exotic film lamination structure impedes backside physical attacks [9] They require additional die or layer, which causes an increase in the size of an IC chip.
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